Memory is one type of integrated circuitry, and is used in systems for storing data. Memory is usually fabricated in one or more arrays of individual memory cells. The memory cells are configured to retain or store information in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Integrated circuit fabrication continues to strive to produce smaller and denser integrated circuits. Accordingly, there has been substantial interest in memory cells that can be utilized in structures having programmable material between a pair of electrodes; where the programmable material has two or more selectable resistive states to enable storing of information. Examples of such memory cells are phase change memory (PCM) cells.
PCM cells may comprise selectable memory states corresponding to a high resistance state (HRS) and a low resistance state (LRS). Traditional PCM cells have a phase change material (for instance, a chalcogenide; such as a so-called GST material comprising a mixture of germanium, antimony and tellurium) as the programmable material. In operation, a portion of the phase change material is altered in phase in the HRS state relative to the LRS state. For instance, the portion may be amorphous in one of the states, and crystalline in the other. Accordingly, the PCM cells may be transitioned between the HRS and LRS states by melting a region of phase change material, and then either crystallizing the material or amorphizing the material.
Performance characteristics of a memory cell may degrade over multiple cycles of transitioning between the HRS and LRS states. Accordingly, it is desired to develop memory cells which may have improved endurance.